How Far Could Gps Go in Monitoring Structural Response to Wind Events?

Two techniques have been applied increasingly in recent years for monitoring the response of tall buildings to wind: the traditional accelerometer and GPS. The focus of this paper is to study how the two sensors perform relative to each other, and in particular the value of GPS measurements in improving wind effect modelling. The test site is a 192m high office tower in downtown Sydney (with a height of 222m to the tip of the spire). It is 45 levels above ground and has 20m of underground levels, and was completed at the end of 2004. Accelerometers and anemometers have been installed on the tower since 2005, and in the middle of 2006 GPS was added to the monitoring system. Data from three reference stations in the SydNET GPS CORS network have been analysed together with data from the GPS rover on the tower, forming baselines of 1.1km, 5km and 21.1km in length. Large wind events were captured by the system on 7 September and 15 November 2006. The analysis will focus on the dynamic response to wind events derived from displacement measured using three GPS reference stations, how to validate GPS-derived resonant response with accelerometer measurements, and how to separate the static and quasi-static components from the GPS measurements. The full picture of structural response to wind will be established by combining the static and quasi-static components with the validated resonant component. It has been demonstrated that the resonant response obtained from both GPS and accelerometers agree well with each other. The full-scale structural fundamental mode of natural frequencies is 0.25Hz for the NS direction and 0.29Hz for the EW direction, with a first torsional frequency of 0.41Hz. It is encouraging that results using the GPS reference station 21km away from the rover also captured the 0.25Hz resonant signal very clearly. Such information offers structural engineers the opportunity to refine their FEM analysis and develop models more representative of the real structure.